The present invention relates generally to ovens and cool-off tunnels for curing and cooling painted objects and more particularly to a top entry oven for curing automotive vehicle bodies that have received a first or prime coat of paint.
It has been common practice within the automotive industry that after the prime coat layer of paint has been applied to an automotive body, such automotive body is moved through a drag-through oven to cure the prime coat and then through a cool-off tunnel Drag-through ovens are characterized by excess heat loss, increased contamination to the surrounding environment, and more importantly are not able to uniformally raise the temperature of the skin of the vehicle body thereby producing hot spots in some areas and uncured paint in others. Further, the time to cure the painted body (cure time) of these ovens is relatively long due to its inherent inefficiencies requiring a long heat soak period to permit heat to reach hidden body areas.
A further drawback of prior ovens is that they employ a direct gas fired convection air zone utilizing high volumes of recirculated air requiring large filtration units to filter 100% of the air to decrease the probability of dirt contaminating the uncured paint. Additionally, during the cure process solvents are emitted from the paint and enter the recirculation ducting where they become deposited. Deposited and condensed solvents are a major source of dirt contamination since, as mentioned, they are located throughout the ductwork, both before and after the filtration unit. Major and costly cleaning operations are required during production shutdown periods to remove this buildup.
As mentioned, another drawback of this type of system is the excessive time required for oven heat-up as well as cool-down prior to and at the end of a production run. Normal oven heat-up and cool-down times are approximately one hour each. This long heat-up/cool-down requirement represents a considerable waste of energy. In addition, due to the construction of these ovens, vehicle bodies cannot be easily removed until the oven cools down. Consequently, if there is a production stoppage the vehicle bodies must remain in the oven during such stoppage resulting in damage and overcuring of the paint. In addition, if the production stoppage results from a problem inside the oven personnel can not enter the oven to investigate the problem until the oven has cooled down, one hour later.
It is an object of the present invention to provide an oven that can be used to both cure and cool a vehicle body and an oven characterized by reduced cure and cool times. A further object of the present invention is to uniformly and evenly distribute heat to the painted vehicle body. A further object of the present invention is to reduce heat loss and smoke and solvent contamination in the oven and to the surrounding environment thereby reducing maintenance intervals. A further object of the invention is to cure and cool a body without recirculating airflow. An additional object is to eliminate the requirement for lengthly oven heat-up and cool-down cycles thereby eliminating the need to remove the bodies from the oven during production stoppages. A further object of the present invention is to provide an oven in which the temperature curing profile can easily be varied to accomodate a staggered production line of varying body styles which may enter such oven in a sequential or predetermined manner. An additional object of the present invention is to provide an oven having reduced energy consumption.
Similar ovens have also been used to cure the top coat layer of paint. One known deficiency in top coat painting is that this layer of paint exhibits dripping or sag on vertical surfaces form gravity. It is a further object of the present invention to produce an oven in which the object to be painted is oscillated (or rotated) during the oven curing process which reduces paint sag on painted vertical surfaces. With paint sag reduced or eliminated, thicker paint coatings can be applied providing a higher quality and a more durable finish.
Accordingly the invention comprises: an oven system for curing and cooling a painted vehicle body, the oven comprises: a lower structure defining an open top, a bottom, opposing end walls and side walls extending upwardly from the bottom. The side walls may include inwardly directed portions and the side and end walls cooperate to define the open top. The bottom, end walls and side walls may be thermally insulated to prevent heat loss. The oven is adapted to receive a separate carrier cover that can be raised, lowered and transferred relative to the open top to enclose the oven when positioned thereon. The carrier cover includes means for oscillating or rotating the body to by cured and/or cooled relative to lamps and air flow. The oven and/or system additionally includes first duct means, for supplying fresh cooling air, at a first volume, into the interior of the oven and for exhausting such air therefrom. The first duct means may include a first air duct supported by one of the side walls and a second air duct supported by the other of the side walls, such ducts extending substantially along the length of side walls and spaced from the bottom and from the underside of the inwardly directed portions of the side walls. Each of the first and second air ducts may include at least one longitudinally extending outlet passage. Second duct means are provided for supplying fresh curing air at a second preferrably higher volume to the interior of the oven and for exhausting such air therefrom. This second duct means may include a first plurality of air ducts supported by the first air duct, a second plurality of air ducts supported from the second air duct and a third plurality of air ducts supported upon the bottom. Each of the air ducts of the first, second and third plurality of air ducts extend longitudinally along the length of the oven; and include an open side through which is air communicated to the interior of the oven. A plurality of infra-red heating lamps are supported relative to the air ducts and positioned relative thereto such that cure air flows across lamps. Non-contacting temperature sensors are provided to sense body skin temperature and assist in its regulating lamp output to control optimum curing of the paint.